The invention relates to a product (multiplier) circuit and more particularly to a product circuit such as used in an FM quadrature detector.
Among various types of FM detectors, quadrature detectors have been extensively employed because as they are suitable for implementation on an IC chip and hence desirable in terms of their cost. Such a quadrature detector includes a double-balanced type differential amplifier. A product signal output obtained from the differential amplifier is amplified by a post amplifier and thereafter delivered to a low-pass filter.
Fundamental performance properties of an FM receiver such as the S/N ratio and the distortion are primarily determined by the characteristics of the desired FM detector stage. Accordingly, it has long been desired that the S/N ratio in the double-balanced type differential amplifier of the product detector section be improved.
Accordingly, an object of this invention is to provide an improved product circuit particularly suited for use in a quadrature FM detector which provides an improvement in the S/N ratio whereby fundamental performance properties of the FM receiver are improved.